The invention relates to the control of motor vehicle power trains and in particular to the control of their cooling circuits.
It is known that hybrid vehicles are equipped with a power train comprising a combustion engine, one or two electrical machines, power electronic components and a power battery.
The combustion engine can be used to recharge the batteries via a generator and/or to provide the vehicle with traction or propulsion. When the combustion engine simply recharges the vehicle batteries, it is said to be a series hybrid vehicle. When the combustion engine provides the vehicle with traction and/or propulsion, it is then said to be a parallel hybrid vehicle.
Whatever the architecture connecting the combustion engine and the electrical machine or machines, it is necessary to cool the combustion engine, the electrical machine or machines, and the power electronic components.
However, the temperature level required for the liquid used to cool the electrotechnical components (the electrical machine or machines and the power electronic components) and the temperature level required for the liquid used to cool the combustion engine are not the same. Indeed, to improve the reliability of the electrotechnical components (particularly the power electronics), the temperature of the liquid coolant must not exceed a threshold value such as 70° C. Also conventionally, the liquid used to cool the combustion engine must not itself exceed a threshold temperature such as 100° C.
It is therefore advantageous to use two cooling circuits so as to satisfy the thermal specifications of the components of the hybrid power train, namely a low-temperature circuit for the electrotechnical components and a high-temperature circuit for the engine.
The use of two cooling circuits that are entirely separate or are in contact via a degassing vessel means that an additional electric water pump has to be run constantly thus increasing the electrical power consumption of the vehicle, the required life of the electric pump, and its cost. In some instances, it also dictates the use of two degassing vessels.
It will also be recalled that, in the case of engines equipped with a turbocompressor, it has become common practice to use an electric water pump to cool the bearings of the turbocompressor when the engine is not running. It is also necessary to use an electric water pump on a hybrid vehicle in order to maintain comfort levels within the cabin when the engine is not running when the vehicle is stationary or when driving under electrical power.
Document JP-2004 07 66 03 discloses a vehicle in which the two cooling circuits associated respectively with the engine and with the electric motor can be placed in fluidic communication if the pump belonging to one of the circuits should fail. The establishing of communication is restricted to this abnormal circumstance.